Process for the production of nitrides suitable for ceramic materials

Abstract

A process for the production of nitrides for ceramic materials, in particr ALN, is described in which the element to be converted to the nitride is anodically oxidized. This oxidation is carried out in the presence of a nitrogen compound which can be reduced under the electrolysis conditions and of a substance which increases the conductivity. The electrolysis is followed, if necessary, by removal of volatile constituents and calcination of the product.

What we claim is: 
     
       1. A process for the production of nitrides or nitride precursors for ceramic materials, which comprises anodically oxidizing by electrolysis at least one element of said ceramic materials in the presence of at least one nitrogen-containing compound which is reduced during said electrolysis, and at least one conducting salt which increases conductivity, wherein said at least one ceramic material element is selected from the group consisting of Ca, Mg, B, Al, Ga, Si, Sn, V, Ti, Zr, Cr, Mo, W, Y, Nb, Ta, Zn and the lanthanides and mixtures thereof. 
     
     
       2. The process as claimed in claim 1, wherein the element is selected from the group consisting of B, Al, Si and Ti. 
     
     
       3. The process as claimed in claim 2, wherein the element is Al. 
     
     
       4. The process as claimed in claim 1, wherein the nitrogen-containing compound comprises a primary or secondary, aliphatic, aromatic or araliphatic amine or NH 3  or mixtures thereof. 
     
     
       5. The process as claimed in claim 4, wherein said aliphatic group is a C 1  -C 12  alkyl group, C 3  -C 10  cycloalkyl group or a C 2  -C 10  alkylene group which is uninterrupted or is interrupted by a heteroatom. 
     
     
       6. The process as claimed in claim 4, wherein said aromatic group is a C 6  -C 20  aryl group. 
     
     
       7. The process as claimed in claim 4, wherein said araliphatic group is a C 6  -C 20  aryl group having a C 1  -C 12  alkyl substituent. 
     
     
       8. The process as claimed in claim 1, wherein the conducting salt, which increases conductivity, comprises at last one ammonium salt of the formula:   R.sub.3 NR'.sup.+ X.sup.-     wherein the R radicals, which are the same or different, are straight-chain or branched-chain alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, aralkyl or aryl groups, or two R radicals together form an alkylene group, R' represents hydrogen or has the same definition as for said R radicals, and X is F, Cl, Br, I, ClO 4 , BF 4  or PF 6  or a mixture thereof.   
     
     
       9. The process as claimed in claim 8, wherein R is alkyl, and R' is hydrogen or alkyl. 
     
     
       10. The process as claimed in claim 1, wherein the electrolysis is performed in the presence of a polar, aprotic solvent. 
     
     
       11. The process as claimed in claim 10, wherein said polar, aprotic solvent is a nitrile or an alkylene carbonate or a mixture thereof. 
     
     
       12. The process as claimed in claim 11, wherein said alkylene carbonate is ethylene carbonate or propylene carbonate. 
     
     
       13. The process as claimed in claim 1, wherein the volatilizable constituents are removed after the electrolysis. 
     
     
       14. The process as claimed in claim 13, wherein said volatilizable constituents are removed by heating or under reduced pressure or by a combination thereof. 
     
     
       15. The process as claimed in claim 13, which further comprises adding sintering agents, ceramic fibers, whiskers or ceramic powders or mixtures thereof to the electrolysis mixture before or during the removal of the volatile constituents. 
     
     
       16. The process as claimed in claim 1, wherein the electrolysis mixture is heated to at least 500° C. 
     
     
       17. The process as claimed in claim 16, wherein the electrolysis mixture is heated to at least 500° C. after removing the volatile constituents. 
     
     
       18. The process as claimed in claim 17, wherein the electrolysis mixture is calcinated at temperatures from 600° to 1,300° C. 
     
     
       19. The process as claimed in claim 18, wherein the electrolysis mixture is calcinated at temperatures from 750° to 1,100° C. 
     
     
       20. The process as claimed in claim 18, wherein said calcination is conducted under vacuum or protective gas. 
     
     
       21. The process as claimed in claim 20, wherein said protective gas is selected from the group consisting of nitrogen, argon, ammonia and mixtures thereof.